Definition. Options IV Percentile (1 Month) is the fraction of trading days in a rolling window where the 1-month ATM implied volatility was below the current level. Returns rolling windows of 30, 100, and 365 days.

Interpretation. A value of 0.9 means current IV is higher than 90% of observations in the window, while a value near 0 means current IV sits at the low end of its recent range.